Being able to bunny hop is a useful skill. Once in a while you just don't have the time or the space to go around something. Once in a great while, your best evasive maneuver involves going over something.

The comments about tacoing your wheel are well taken. Never straighten your legs when you bunny hop; let them absorb some of the impact on landing. Done properly, the landing should be very smooth.

Unfortunately, it's not really something you can't practice on grass if you have a road bike.